Process of treating rubber and products obtained thereby



Patented Apr. 21, 1931 UNITED STATES PATENT OFFICE SIDNEY M. CADWELL, OF LEONIA, NEW JERSEY, ASSIGNOR TO THE NAUGATUCK CHEML CAL COMPANY, OF NAUGATUCK, CONNECTICUT, A CORPORATION OF CONNECTICUT A PROCESS OF TREATING.RUBBER AND PRODUCTS OBTAINED THEREBY No Drawing. Original application filed March 2, 1928, Serial No. 258,670. Divided and this application 4 filed March 2, 1928.

This invention relates to the treatment of rubber and similar materials and to the products obtained thereby. The invention is more particularly concerned with new classes of 5 chemical compounds capable of functioning as accelerators of vulcanization. This case is a division of copending application Serial No. 258,670, filed of even date.

Accordingly the objects of the invention include the vulcanization of rubber treated with the hereinafter described classes of compounds. Another object is to provide new chemical compounds, particularly useful in vulcanization, which are comparatively inexpensive and at the same time highly efficient both from the standpoint of their behavior during the compounding of rubber as Well as in the properties which they impart to the vulcanized product. Another object of the invention is to accelerate the action of the new chemical compounds by the addition of base or to retard their action by the addition of acid material. A further object of the invention is to provide a method whereby the acid or base or the new compounds themselves may be introduced into rubber.

In the present practice of the use of accelerators, it is generally known that many of the compounds employed are so powerful that they cause a prevulcanization, or burning on the mixing mill. This serious disadvantage is possessed by many of the accelerators which have the property of vulcanizing rubber at ordinary temperatures or at temperatures Well below those ordinarily employed in hot vulcanization, for example at 212 F. or thereabouts. Illustrations of such rapid accelerators are metallic dithiocarbamates, metallic salts of other thioacids, mercapto thiazoles and the like. According to the present invention this serious objection of prevulcanization may be entirely overcome, the rubber compounds may be mixed upon the mill with practically no danger of Serial N 0. 258,677.

prevulcanization thereon, without sacrificing the accelerating power Which is desired. Certain of the compounds forming the subect matter of the present invention may be mixed with rubber with entire safety on the mixing mills, subject to the conditions hereinafter named, whereas others may be safely rapidly as diphenyl methyl dimethyl dithiocarbamate reacts under the same conditions. The invention includes treating rubber with a compound containing the group RcsY, 1||I where and X are sulphur and nitrogen respectively, i. e.,

SCSY.

The invention further includes the products thus obtained, and also the preparation of the chemical compounds themselves.

The invention further consists in accelerating the action of the compounds by the addition of basic materials and in retarding the action of the compounds and particularly the burning of the compounds by the addition of acid material. The invention further consists in introducing basic materials or acid materials or the compounds herein disclosed by diffusion from rubber or from any surrounding medium.

The thiazoles subject of the present invention are shown as having the hydrogen of the mercapto or mercaptan group substituted by the following organic groups:

2-4 dinitrophenyl, 2-6 dinitro 4 chlor phenyl, picryl, triphenylmethyl, trimethylmethyl, phenyl methtylene bis, benzal bls, allyl, phenyl chlor meth lene bis. The substitution is on the Y o RUBY.

The compounds contain the group -sosY,

and may be written The first three of these groups have one nitro group ortho to the bond connecting the phenyl grou with the CS group, and at least one of t e remaining substitutents meta to the nitro roup. In the diniti'o phenyl compounds, the two nitro groups are meta to each other, and one of them is ortho to the bond connecting the phenyl group with the CS group in the accelerating substance.

In all cases the entire compound reacts at least as rapidly with sodium hydroxide in boiling aqueous alcohol as diphenylmethyl dimethyl dithiocarbamate reacts under the same conditions. All the compounds WhlCh react with sodium hydroxide at least as rapidly as diphenylmethyl dimethyl dithiocarbamate, accelerate vulcanization, in the presence of a metallic oxide, such as zinc oxlde or an equivalent metallic compound.

Zinc oxide is a good illustration of a metallic oxide which may be used. In place of zinc the following elements-may be used in any combined form preferably somewhat basic and soluble in rubber mercury preferably in the mercuric state, lead preferably in the plumbous state, cadmium, copper preferably in the cupric state, arsen c preferably n the arsenous state, manganese. preferably 1n the manganous state. Preferably themetallic compound is of such a nature'that the metallic element is available during the vul canization process. Oxides,"st earates, carbonates are among the metallic'compounds which may be used.

As an embodiment one may mix of pale crepe, 10 parts of zinc oxide',i3parts' of sulphur and 1 A; parts of 2,4 dinitrdpheuyl benzothiazylsulphide. This stock resists burning on the mill and is well vulcanized after heating for 60 minutes under 20 pounds'i steam pressure or for 60 minutes under 40;

pounds steam pressure. This stock does not deteriorate as rapidly as similarstocks-em.

ploying other accelerators suchj slthe 1dimethyl dithiocarbamate compound forine,

stance.

The 2-4 dinitrophenyl benz litharge.

The 2-4 dinitrophenyl benzothiazylsulphide may be prepared as follows:

40 grams of sodium hydroxide are dissolved in 500 rams of water and 168 ams of mercapto enzothiazole and 500 cc. of

95% alcohol are added. The mixture is may he prepared in like manner, that is reacting the solution of the sodium salt of the thioacid or thiazole with a chloride of the group Y. In the case of picryl benzothiazyl sulphide the chloride would be trinitrochlorbenzol instead of dinitrochlorbenzol.

The compounds disclosed herein function Well when the cure is carried out according to any of the commercial methods such as in steam, talc 'water, etc.

I have observed that the action of the compounds disclosed herein is accelerated by the presence of; a small amount of a basic material such as sodium hydroxide, trisodium phosphate, dicyandiamide, piperidine, aniline, dibenzylamine, piperazine hydrate, triethanolamine. stances is particularly marked in the case of the polynitrophenyl compounds such as 2, 4 dinitrophenyl benzothiazyl sulphide. The use of the base lowers the temperature at which the accelerator functions or increases its speed of functioningand usually increases the tensile strength at all temperatures of vulcanization by about 10%.

The base may be employed in amounts generally less than 1% or thereabouts.

The effect of the alkali on these dinitrophenyl compounds is much more marked than lit is upon other accelerators such as tetramethylthiuram monosulphide, diphenylguanidine, acetaldehyde aniline condensation product or heptaldehyde aniline condensation product.

' Since a basic substance accelerates the action of the accelerator and lowers the tem- Iperature at which it functions, it also increases the speed of burning on the mixing jrazy'l; sulphide works well in air curesgand'withw "mill. Therefore the greater the amount of base present in the mix, the greater the danof burning'on the mixing mill and rub- The action of the basic subexpression also includes the burning, scorching, or setting up of the stock onimills, calen' ders, tubing machines, as well as any prevulcanization which may occur or be incip ient prior to the actual deliberate vulcanizak v v parts of pale crepe, 10 parts of zinc oxide, 3 parts of sulphur 'and2Iparts ofdinitrophenyl tion operation. This is particularly true of the dinitrophenyl compoundsz On the other hand the additidnof acid re tards the action of the acceleratonand there:

fore improves-"its resistance to burning. ;.;He1'+e again the action .Eis particularly marked in the case'o'f the polynitrophenyl compoun instance .1

added'to the stockgiven above "so'gefi'e'cts the; afct, on. of the accelerator-that. after so in-*i I For part 0:5 monochlor acetic acid at 5 pounds'stearn pre'ssure', no cure'w as n'ed I and afterljfiQ. minutes at 40 "pounds no f'curewas obtained even a-ft'er 60 minutes.

1 which I have, successfully employed are *sul "I jipermit the. J5

-or neutralized.-.

phanilic, oxalic, picric, phosphoric, trichlorf acetic, para toluene sulphonyl chloride and pine tar. I have also successfully employed substances which may form acids during the course of vulcanization suchi as ethyl oxalate or zinc acetate. I Q a Since the presence of -acid reta-rds'theaction of compounds; disclosediherein and particularly the action ofgthei .polynitrophenyli' compounds, the addition .of'l'an appropriate amount of acid serves" to increase the'resistance to burning 'so much-a's maybe desired;

Mixes which are slightly ac'idbecause ofthe presence of ensemble; I burning on the m'ilLIQb vulcanization of rljibbe so Well by vtheilier ein lesc I I unless theacidi'cf Likewise, rubber' are appreciably. ba, basic materials, may. di sp undesirable tendency "towards tion. Such basic). rubbers go treated with" acidic materi I I curb, or to controlthis-tnde y topre'iml: canize. Therefore, by the use of basic 1 material and acidic material in suitable propor tions as required, any rubber or stock may be brought to canization.

basic materials-intended to activatethe com.

7 nds .Or?accelerate tl eir action,- one iriays; .=inaterialito difl'use into" the rubber., ,-,Fo "instance if the 'stock. "given above for vu can" tion. intheairbeyulcan- I I "pressuretheftensile iyas 2380 poundsa If .5;part of. monochlor acetic acid were used- 7 pounds" disclosed of 2,4 diiiitr,

' to formjon "oxide, 3 parts'ofisu lphu benz ylamine; I I 'imll' iinitheiusual' manner and calendered to a lowed to stand for 24 hours-t0 I fusion of the ,dibe'nzylami'ne I I I yf'trophenyl stock and of the dinitrophenyl nature; or contain apprec ableamounts f acid or acidicpingrcdients," isno a" ccelerated.v v I I 1eatedat-212 and it isfifoii d. that vult liot I the] dibenzylamine jf acts monochlor acetic acid las -w I dinitrophenyl benzo thia i 'Aspointed out'before the presence of the monochlor'aceticacid improyes the resistance Instead Ofaddingon ftheiinixing r ll h I ized in air containing ammonia, the vulcanization is greatly accelerated and the surface of the stock is remarkabl hard and resistant to marring. The intr uction of the basic ,material may be made on the .mill by diffusion I from aliquid, solution, or gas, or from adjoining rubber stock or from a fabric. I

I As another example, I make the compounds inthe usual-manner consisting of 100 benzo thiazy'lsulphide. This stock in the form of a sheet .060 thick-or intheform of an article may be treated with gaseous arnmonia for 16 hours. Thereafterit will vulcanize sat-212 F., much more rapidly than a stock not so treated. lnsteadof gaseous amtroduction Zby' L tration; is given 7 parts of zinc .oxide ff I I I U henylbenzojthiazyl sulphide, onb chllp aceticacid are mixed thicknessfot- 1 Anothfer' 'stock is made up of 100 parts "'ipale' crepe; 10 parts of zinc I I and 4: parts of di- Th'i's'iqjstbck is mixed on the thickiie o r The. tw"

{stocks are plied f each and alpermit the dif- 'into the diniup namely benz o thiazylsulphide into thedibenzylamine stock."--Thereafte rgthe plied stock is 'a'ni z' a-tio'n' occurs] much more'fquickly than dosfforjtheindividual stocks which have been plied up. It ill be observed that Q-neutralize the to activate the ii'lphide.

to burning buttheprocedure' may be carried out without the-use be the acid:

I T substitutedflfor thecompounds given above. Predeterminedfspeed' of. vul- The basic'inatjerialg; mmoiiia. etc.) may be $11 minding medium ntralize the acid, celerator. For inis calendered to a will activate the dinitrophenyl compound. The basic material may be introduced in any desired manner at any time prior to complete vulcanization, i. e., it may be introducedduring vulcanization as a gas or vapor, or it may be applied to the stock by painting, dipping, or blending in cement form etc. before the stock is subjected to vulcanization, or the stock may be vulcanized in a solution or suspension of the basic material.

Any of these ingredients, base, acid, and accelerator may be brought together in the form of cements, i. e. a cement containing accelerator may be mixed with a cement containing the base at the time the cement is to be used. The accelerator cement will not vulcanize appreciably at ordinary temperatures if the base be absent. Likewise, an accelerator'containing cement may be preserved in an unvulcanized condition for a long period by the addition of acid (as such, in solution, or in a cement). When vulcanization is desired, a base may be added (as such, in solution, or in a cement) and vulcanization will then take place.

It is believed that the dinitrophenyl compounds are particularly susceptible to the action of acids and alkalies because the dinitrophenyl compounds of all sorts of acids such as dimethyl dithioca-rbamic acid or bydrochloric acid do not hydrolyze in acid solution but do hydrolyze only in alkali solu: tion.

Further examples include organic derivatives of thiazoles.

Picryl benzothiazyl sulphide (M. P. 152 C.) the probable formula of which is:

G S N0z @N/ {3 sulphide.

are joined, as part of a ring. In this instance the general formula may be Written and more specifically All of the above compounds are new chemicals, not recorded in the literature. The preparation of these materials forms the subject matter of separate applications.

All of the above mentioned compounds are accelerators of vulcanization. Some of them give high tensile strength and other valuable physical ropertics such as improved resistance to abrasion, ageing, and other properties. The claims are therefore to be broadly interpreted as including such treatment of rubber in any form (solid, solution, dispersion) for these purposes as Well as for vulcanization, in which latter instance, it is understood that a vulcanizing agent and a metallic oxide or its equivalent will be added to the rubber. It is of course understood that not all of these compounds are of equal accelerating strength, pound for pound, under identical vulcanizing conditions. These accelerators may be used in conjunction with any of the known antioxidants, age improvers, and other materials introduced into rubber to improve ageing and other physical properties.

Diphenyl methyl benzo thiazyl sulphide and allyl benzo thiazyl sulphide may also be classed as accelerators, but the degree of acceleration is very small, and at present is regarded as of no commercial importance. Methyl benzo thiazyl sulphide is one example of a compound Which does not hydrolyze as rapidly as diphenyl methyl dimethyl dithiocarbamate in the herein described test, and the pure compound did not accelerate vulcanization under the conditions given above as examples.

The compounds in general may be used in amounts varying between and 4 parts on 100 parts of rubber, depending of course on the type of stock, etc.

The rate of reaction of the compound with sodium hydroxide in boiling aqueous alcohol may be determined as follows:

.00125 moles of the compound is weighed into a cc. Erlenmeyer; 25 cc. 95% alcohol and .00125 moles sodium hydroxide in the form of an approximately normal solution are added and the solution brought to the boiling point as quickly as possible and kept there for exactly 30 minutes. The solution is then cooled quickly and titrated with approximately N/lO acid, using phenolphthalein as the indicator. larbon dioxide-free water should be used throughout. A blank should be run in order to check up on the amount of acid necessary to neutralize the sodium hydroxide when no compound is used. The decrease in hydroxyl ion content during the boiling is taken as a measure of the extent of the reaction with sodium hydroxide.

The above procedure constitutes a method .whereby the relative rate of hydrolysis of any given compound of the types disclosed may be compared with that of diphenylmethyl dimethyl dithiocarbamate.

The diphenylmethyl dimethyl dithiocarbamate ma be prepared in accordance with the genera procedure indicated herein, that is reacting an alcoholic solution of a salt (preferably the sodium salt) of dimethyl dithiocarbamic acid with diphenyl chloromethane. Diphenylmethyl dlmethyl dithio carbamate separates as an oil which solidifies and crystallizes on standing over night and may be purified by recrystallization from alcohol. It has a melting point of 96.5-97 C.

It is known that the rate of hydrolysis of organic compounds, or more exactly, their rate of reaction with a base such as sodium hydroxide varies with the substituent in the organic com ound. This variation has been utilized in t e present invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent 1. A rubber product derived from rubber combined with a metallic oxide, a vulcan1z-' ing agent and a compound comprising the group Y being a trinitroghenyl group, which said compound is capa le of hydrolyzing at the SY bond in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

2. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and a compound comprising the group R being an ortho-arylene group, which said B being an ortho-arylene group, which said compound is capable of hydrolizing at the S-trinitrophen 1 bond in aqueous alcohol in the presence 0 sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

5. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and a 2-4-6 trinitrophenyl benzo thiazyl sulphide.

6. A method of treating rubber which coinprises vulcanizing rubber containing zinc oxide and sulphur in the presence of a 2-4-6 trinitrophenyl benzo thiazyl sulphide.

Signed at New York, New York, this 23rd day of Februar 1928.

IDNEY M.-CADWELL.

3. A method of treating rubber which com- I prises vulcanizing rubber containing a metallic oxide and a vulcanizing agent in the pres ence of a compound including the group Y being a. trinitrophcnyl group, which said compound is capable of hydrolizing at the SY bond in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

4. A method of treating rubber which comprises vulcanizing rubber containing a metal- 

